Abstract Prions are infectious, self-propagating protein aggregates that have been implicated in a number of devastating neurodegenerative diseases known as transmissible spongiform encephalopathies. In humans, the most common TSE, Creutzfeldt-Jakob disease, typically strikes without warning, leading to death within 1 year of diagnosis for 90% of patients. The TSEs have been attributed to a specific cellular protein (PrP) that has the potential to convert to a highly structured, ? sheet-rich aggregated form (referred to as amyloid) that is thought to be the infectious agent. With no therapies that can affect either the outcome or progress of the disease, new experimental avenues are crucial. The objective of the proposed research is to mobilize bacterial genetics as a new experimental system for studying prion behavior. Having shown that the E. coli cytoplasm can support the formation of prion-like aggregates, we propose to develop a set of transcription-based genetic assays that can detect conversion of protein domains to the prion state. Using these assays, we will conduct mutant screens to identify cellular chaperones and other factors that can affect the prion process. Because of the evolutionary conservation of chaperone proteins, such screens may uncover potential new drug targets relevant to mammalian disease. We will also use bacteria-based genetic assays to screen bacterial genomes as well as the genomes of higher organisms (including mammals) for novel prion proteins. The discovery of bacterial prions could have profound implications for human health, particularly in the context of host-pathogen interactions. Finally, we envision using bacteria-based genetic assays to screen for small molecules that can hinder conversion to and/or propagation of the prion state. While our primary focus is prion disease, the tools we aim to develop should also be applicable to the large number of non-infectious neurodegenerative diseases that are associated with the formation of amyloid aggregates.